1. Field of the Invention
This invention relates to a discharge lamp unit which applies a high voltage to a discharge lamp .such as a metal halide lamp at the start of lighting, to light up the lamp.
2. Description of the Related Art
In general, the above-described type of discharge lamp unit generates a high voltage ranging from a few kilovolts to a few tens of kilovolts using a high-voltage generation circuit and applies the generated high voltage to the discharge lamp at the time of lighting, to discharge the lamp instantly. Once the lamp lights up, the discharge lamp unit keeps applying a low voltage of a few tens of volts to the lamp so that the lamp can be kept lit continuously.
Thus, if the unit is started with the discharge lamp having been removed when, for instance, the lamp needs to be replaced by a new one, a high voltage will be applied to the cap holder of the lamp. This has necessitated that the cap holder and its peripheral section withstand such a high voltage. For this purpose, the cap holder and its peripheral section have been enlarged or materials having high voltage withstanding characteristics have been employed, thereby resulting in an increase in costs.
To solve the above problem, a suggestion for a discharge lamp unit having a start and lighting circuit, containing a high voltage circuit below the discharge lamp in the same unit has been made (for instance, refer to U.S. Pat. No. 4,574,219). However, with such a discharge lamp unit, the unit itself becomes larger and the entire unit must be replaced to change a bulb.
In Japanese Patent Laid-Open No. Hei. 6-119911, a discharge lamp unit having only a starting circuit booster transformer in the same unit was introduced. However, with this type of unit, at least four connecting wires and connectors were required in the bottom of the discharge lamp, resulting in increased size of the unit.
Furthermore, in Japanese Patent Laid-Open No. Hei. 4-293630, a discharge lamp unit having a connection detection circuit which detects whether the discharge lamp is connected to the cap and shuts off the high voltage supplied to the cap holder if the cap of the discharge lamp is not connected to the cap holder, to prevent application of high voltage when the lamp is not connected, was introduced. However, a special connection detection circuit and detection wires to connect such a circuit to the cap holder were required, thus making the structure complicated.